The optical properties of electrochromic materials change in response to electrically driven changes in oxidation state. Thus, when an applied voltage from an external power supply causes electrons to flow to (reduction) or from (oxidation) an electrochromic material, its transmittance properties change. In order to maintain charge neutrality, a charge balancing flow of ions in the electrochromic device is needed. By enabling the required electron and ion flows to occur, an electrochromic device utilizes reversible oxidation and reduction reactions to achieve optical switching.
Conventional electrochromic cells comprise at least one thin film of a persistent electrochromic material, i.e. a material which in response to the application of an electric field of given polarity, changes from a high-transmittance, non-absorbing state to a low-transmittance, absorbing or reflecting state. Since the degree of optical modulation is directly proportional to the current flow induced by the applied voltage electrochromic devices demonstrate light transmission tunability between high-transmittance and low-transmittance states. In addition, these devices exhibit long-term retention of a chosen optical state, requiring no power consumption to maintain that optical state. Optical switching occurs when an electric field of reversed polarity is applied.
To facilitate the aforementioned ion and electron flows, an electrochromic film which is both an ionic and electronic conductor is in ion-conductive contact, preferably direct physical contact, with an ion-conducting material layer. The ion-conducting material may be inorganic or organic, solid, liquid or gel, and is preferably an organic polymer. The electrochromic film(s) and ion-conductive material are disposed between two electrodes, forming a laminated cell.
When the electrode adjacent to the electrochromic film is the cathode, application of an electric field causes darkening of the film. Reversing the polarity causes reversal of the electrochromic properties, and the film reverts to its high-transmittance state. Typically, an electrochromic film, such as tungsten oxide is deposited on a substrate coated with an electroconductive film such as tin oxide or indium tin oxide to form one electrode. The counter electrode is typically a similar tin oxide or indium tin oxide coated substrate.
As a voltage is applied across the electrodes, ions are conducted through the ion-conducting material. To ensure reliable operation, the ion-conducting material layer generally must be sealed so as to maintain its water content within a range sufficient to provide required ion conductivity. Absent an adequate seal, moisture loss or gain from/to the ion-conducting material layer may adversely impact performance. The instant invention addresses this need by providing a molded edge seal that impedes moisture ingress and egress to/from the circumferential edge region of a laminated device, particularly a laminated electrochromic device.
U.S. Pat. No. 4,174,152 to Giglia, et al., discloses electrochromic devices wherein the polymeric electrolyte material is a hydrophilic copolymer of a selected acrylate or methacrylate monomer and a selected acid group containing a monomer, such as 2-acrylamido-2-methylpropanesulfonic acid.
U.S. Pat. No. 4,335,938 to Giglia discloses electrochromic devices having a layer of tungsten oxide in contact with a layer of organic electrolyte resin comprising a hydrophilic layer of 2-acrylamido-2-methylpropanesulfonic acid homopolymer and an electrode means for changing electrochromic properties of the device.
U.S. Pat. No. 5,433,810 to Abrams discloses a method and device for bonding composite eyeglass lenses. This reference is silent regarding sealing the edges of composite lenses.
U.S. Pat. Nos. 4,361,385 and 4,478,991 to Huang, et al., disclose electrochromic devices having a layer of electrochromic tungsten oxide in contact with a polymeric electrolyte wherein the stability and speed of the device are improved by using a copolymer of 2-acrylamido-2-methylpropanesulfonic acid and vinyl sulfonic acid as the polymer electrolyte. The polymer mixture is cast, dried and hydrated in contact with the electrochromic film, and then a second electrode consisting of paper-carbon is pressed against the polymer layer with a second tin oxide-coated glass plate backing the carbon-paper electrode.
U.S. Pat. Nos. 4,554,318; 4,609,703 and 4,670,350 to Rukavina disclose copolymers of acrylic acid and cyanoethylacrylate, including terpolymers with hydroxyethylacrylate, useful as primers for bonding metal-containing coatings to organic polymer substrates.
U.S. Pat. No. 5,471,338 to Yu, et al., discloses lamination of two coated plastic substrates using a layer of polymer which bonds with both coated surfaces to form a composite. Homo and copolymers of 2-acrylamido-2-methyl propyl sulfonic acid (AMPSA) form the ion-conducting polymer layer and are cured using actinic radiation, preferably (UV) light. AMPSA/N,N-dimethylacrylamide (DMA) polymers are preferred, and benzoin methyl ether and diethoxyacetophenone are disclosed as UV initiators.
U.S. Pat. No. 5,327,281 to Cogan discloses the use of an epoxy to seal a cavity formed when a spacer is used to separate electrodes and contain a liquid electrolyte injected between the spaced electrodes. This patent does not disclose or suggest the novel edge seal method disclosed herein.
Copending and commonly assigned U.S. patent application Ser. Nos. 08/995,788 and 08/996,064, filed Dec. 22, 1997, describe electrochromic devices having nubbed edge regions and sealed edge grooves, respectively.